The present invention relates generally to headboxes for paper machines and, more particularly, to a headbox which comprises a distributor beam part, a distribution part connected to the distributor beam part, and a turbulence part which is followed by a slice part, such as a slice-cone part or the like.
With respect to the prior art technology related to the present invention, reference is made to applicant's Finnish Pat. No. 50,260. A headbox is disclosed in this Finnish patent in which the distributor beam is followed by a distributor-pipe part after which a so-called intermediate-chamber part is provided followed by a lamella part, which in turn is followed by the slice-cone part. The lamella part is constituted by several lamellae which are placed in side-by-side relation and which are inclined with respect to the vertical plane. The lamellae define turbulence channels between them having a trapezoidal cross-sectional configuration.
Although the headbox disclosed in the above-mentioned Finnish patent has proven to be quite advantageous in operation, it has been found to be quite expensive in construction, at least in part due to the intricate construction of the lamella part. Another drawback of this prior art apparatus is that the headbox occupies a relatively large space since the lamella part has a relatively long length. Moreover, replacement of the lamella part to provide one best suited for the particular paper or pulp quality which is being produced is inconvenient.
Since the present invention is also suited for use in multi-layer headboxes, reference is also made by way of example to Finnish patent application Ser. No. 801,587, assigned to applicant's assignee, which discloses a multi-layer headbox for a paper machine which comprises two or more pulp suspension flow channels situated one over the other so as to merge within the region of the headbox slice. The flow channels comprise a distributor beam part, a distributor-pipe part or the like as well as flow-equalizing and turbulence parts. The headbox disclosed in this Finnish application is characterized in that between the flow-equalizing part and the turbulence part, there is a heavy plate part which is provided with a set of flow openings and the turbulence part is constituted by several plate lamellae situated in side-by-side relationship and fixed in connection with the plate part substantially only at their forward ends. One or more intermediate plates are located between the sets of plate lamellae and extend to the region of the slice of the headbox.
It is a particular object of the present invention to provide a new and improved headbox in which the lower-lip constructions by means of a unified lower-part frame and in which the above-described lamella part construction is replaced by a construction which is considerably less expensive and which can be readily exchanged in accordance with the requirements imposed by the particular production being run.
With respect to the prior art relating to the present invention, further reference is made to Finnish patent applications No. 801,854 filed June 10, 1980, and Ser. Nos. 802,695 and 802,696 filed Aug. 26, 1980, all of which are assigned to applicant's assignee. It is another object of the present invention to provide a new and improved headbox in which the improvements disclosed in these Finnish patent applications are applicable, where appropriate.
In particular, with reference to Finnish application No. 801,854, a headbox is disclosed having a cassette-type construction, i.e., wherein the turbulence part is constituted by one or more exchangeable grate cassette members. More particularly, this application discloses a grate-shaped turbulence generator situated between the equalizing chamber and the slice cone. However, this construction is not entirely satisfactory in that the flow of the pulp suspension does not change its direction within the zone of the grate member. In this connection, it is generally desirable to change the direction of flow in that, generally, within the initial portion of the headbox, the construction is such that the flow is first directed to slant upwardly whereas the flow is usually discharged in a substantially horizontal direction from the slice cone. Therefore, in accordance with the prior art, the flow direction of the pulp suspension is generally changed within the region of the slice cone. However, since the pulp suspension flow is discharged from the slice cone onto the wire, a change in flow direction which takes place within the area of the slice cone may result in an instability in the flow with resulting flaws being created in the web produced.
Accordingly, it is another object of the present invention to provide a new and improved headbox in which a change in the flow direction of the pulp suspension takes place before the region of the slice cone and wherein the change in direction additionally results in favorable effects, described in greater detail below.
It is also known in the prior art to provide arrangements in a headbox of a paper machine in which step structures are present in the path of the flow of the pulp suspension which increase the turbulence thereof, as well as structures which cause the flow from tubes to be spread into slot-shaped spaces which extend transversely across the headbox. In this connection, reference is made by way of example to U.S. Pat. Nos. 3,528,882, 3,562,107, 3,954,558, 4,070,238, and 4,137,124. Moreover, reference is made to Swedish Pat. No. 214,100, U.K. patent application No. 2,019,465 and to Finnish patent application No. 447/71. However, none of these prior art solutions teaches or suggests the use of the change in direction of the pulp suspension flow as a means to control the flow or to render it advantageous by spreading the flow.